The primary purpose of a safe and arm (S&A) device is to prevent accidental functioning of a main charge of explosive (military or otherwise) in a fuze prior to arming. Typically, in an electromechanical S&A device, a sensitive primary explosive is physically separated from a booster explosive by an interrupter or barrier component. The barrier component, often a slider or rotor, interrupts the explosive path and thus prevents detonation of the booster and main charge prior to arming. Arming occurs by moving the barrier component to align the explosive elements.
In some applications it is desirable to operate a safe and arm device according to a fluid pressure differential, such as in the event of dropping a bomb from an airplane. But if there is a direct link between the barrier component and the pressure differential then the device may be sensitive to pressure fluctuations other than those meant to arm the device. Therefore, there is a need for a safe and arm device wherein the arming of the device is indirectly affected by the pressure differential.